Lithographic apparatus and device manufacturing method

ABSTRACT

A lithographic projection apparatus is disclosed for use with an immersion liquid positioned between the projection system and a substrate. Several methods and mechanism are disclosed to protect components of the projection system, substrate table and a liquid confinement system. These include providing a protective coating on a final element of the projection system as well as providing one or more sacrificial bodies upstream of the components. A two component final optical element of CaF 2  is also disclosed.

This application is a continuation application of U.S. patentapplication Ser. No. 11/529,587, filed Sep. 29, 2006, now U.S. Pat. No.8,208,124, which is a continuation application of U.S. patentapplication Ser. No. 10/927,531, filed Aug. 27, 2004, now U.S. Pat. No.8,208,123, which claims priority from European patent application no. EP03255377.8, filed Aug. 29, 2003, each of the foregoing applicationsincorporated herein in its entirety by reference.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidconfinement system (the substrate generally has a larger surface areathan the final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent application no.WO 99/49504, hereby incorporated in its entirety by reference. Asillustrated in FIGS. 2 and 3, liquid is supplied by at least one inletIN onto the substrate, preferably along the direction of movement of thesubstrate relative to the final element, and is removed by at least oneoutlet OUT after having passed under the projection system. That is, asthe substrate is scanned beneath the element in a −X direction, liquidis supplied at the +X side of the element and taken up at the −X side.FIG. 2 shows the arrangement schematically in which liquid is suppliedvia inlet IN and is taken up on the other side of the element by outletOUT which is connected to a low pressure source. In the illustration ofFIG. 2 the liquid is supplied along the direction of movement of thesubstrate relative to the final element, though this does not need to bethe case. Various orientations and numbers of in- and out-letspositioned around the final element are possible, one example isillustrated in FIG. 3 in which four sets of an inlet with an outlet oneither side are provided in a regular pattern around the final element.

SUMMARY

The use of immersion liquid in the space between the final element ofthe projection system and the substrate means that the final element ofthe projection system (e.g., an ‘abschlussplatte’ which seals theprojection system, or the final optical element of the projectionsystem) and substrate table are in contact with the immersion liquid.This can lead to problems with reaction or dissolution in the immersionliquid of the components of the projection system or substrate table.

Accordingly, it would be advantageous, for example, to provide alithographic projection apparatus in which degradation of components,because of contact with immersion liquid, is reduced.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate using a projection system and havinga liquid supply system configured to at least partly fill a spacebetween the projection system and the substrate with a liquid, whereinan element of the projection system through which the pattern isprojected has, on a surface configured to be in contact with the liquid,a protective coating which is substantially insoluble in the liquid.

In this way, for example, the final element of the projection system maybe made of a material which is selected due to superior opticalproperties and considerations regarding the activity between thematerial of the element and the immersion liquid do not need to be takeninto account. If the thickness of the protective coating is kept low,the effect of the protective coating on the projection beam may beminimized.

In an embodiment, the protective coating is a metal, a metal oxide ornitride e.g. TiN, diamond, DLC or SiO₂. These materials are bothtransparent to projection beam radiation used in immersion lithographyas well as insoluble or inert in the immersion liquid, which in anembodiment comprises substantially water.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate using a projection system and havinga liquid supply system configured to at least partly fill a spacebetween the projection system and the substrate with a liquid, whereinthe liquid supply system is configured to provide a first liquid in thespace in contact with an element of the projection system through whichthe pattern is projected and to provide a second liquid in the space incontact with the substrate.

This arrangement may allow a first immersion liquid to be chosen suchthat the material of the final element of the projection system isinsoluble (and/or inert) in that liquid. On the other hand, a secondimmersion liquid, different from the first, may be selected such that ithas the correct optical properties or otherwise as required. In anembodiment, the first and second liquids are kept apart so that it canbe ensured that only the first liquid is in contact with the element.

In an embodiment, the liquid supply system has a membrane configured toseparate the first and second immersion liquids. This is one of manyways in which the two immersion liquids can be arranged to be correctlyconstrained relative to the final element and the substrate. Material ofwhich the membrane could be made includes quartz, which, in anembodiment, may be between 0.1 and 5 mm thick. In this way, for example,the final element of the projection system may be protected from thesecond immersion liquid with only a small adverse effect to the qualityof the projection beam. Other solutions are possible.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate using a projection system and havinga liquid supply system configured to at least partly fill a spacebetween the projection system and the substrate with a liquid, whereinan element of the projection system through which the pattern is to beprojected and configured to be at least in part in contact with theliquid, comprises first and second components of CaF₂, SiO₂ or acombination of both materials, the components being arranged such thatthe projected pattern passes through the first component before passingthrough the second component.

In this arrangement it is typically the last optical element withoptical power and/or the abschlussplatte which is referred to. In thisway the good optical properties of CaF₂ may be harnessed because asecond component of CaF₂ can be used to cancel out the effect of theintrinsic birefringence of a first component of CaF₂. One way of doingthis is to provide the first and second components with crystal axesaligned such that the intrinsic birefringence of the first component iscompensated for by the intrinsic birefringence of the second component.

In an embodiment, the first and second components are concentric. Thisis a compact geometry in which the optical paths through the firstcomponent are substantially of equal length to those through the secondcomponent. In this arrangement the second component may be positionedsubstantially within a recess in the first component such that if thefinal lens element is substantially of hemispherical shape the secondlens component is substantially hemispherical in shape and the firstcomponent is also substantially of hemispherical shape though with a(substantially hemispherical) recess in the non-spherical surface.

In an embodiment, only the final element of the projection system ismade of CaF₂ and the other elements of the projection system can be madeof materials other than CaF₂.

According to an aspect of the invention, there is provided alithographic projection apparatus arranged to project a pattern from apatterning device onto a substrate using a projection system and havinga liquid supply system configured to at least partly fill a spacebetween the projection system and the substrate with a liquid, whereinthe liquid supply system comprises a sacrificial body, in the liquidupstream of the space, configured to dissolve in the liquid to reducethe rate of dissolution of a component of (a) the projection system, (b)the substrate table, (c) the liquid supply system, or any combination of(a), (b), and (c).

This aspect works by the sacrificial body dissolving in the immersionliquid to reduce the activity of the immersion liquid on componentsdownstream of the sacrificial body. For example, if the sacrificial bodyis made of the same material as the component it is to protect, theimmersion liquid becomes substantially saturated in the material of thesacrificial body such that no more such material can be dissolved by theimmersion liquid and the component made of that material is therebyprotected. One example of such material is quartz.

If the sacrificial body is of a shape with a high surface area to volumeratio (e.g. rods, tubing, fibers), it will dissolve particularly quicklyin the immersion liquid which is advantageous.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationonto a substrate through a liquid provided in a space between an elementof a projection system and the substrate, wherein a surface of theelement in contact with the liquid comprises a protective coating whichis substantially insoluble in the liquid.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationonto a substrate through a first liquid and a second liquid provided ina space between an element of a projection system and the substrate,wherein the first liquid is in contact with the element and the secondliquid is in contact with the substrate.

According to an aspect, there is provided a device manufacturing methodcomprising projecting a patterned beam of radiation onto a substratethrough a liquid provided in a space between an element of a projectionsystem and the substrate, wherein the element is at least in part incontact with the liquid and comprises first and second components ofCaF₂, SiO₂ or a combination of both materials, the components beingarranged such that the patterned beam of radiation passes through thefirst component before passing through the second component.

According to an aspect, there is provided a device manufacturing methodcomprising projecting a patterned beam of radiation onto a substratethrough a liquid provided in a space between an element of a projectionsystem and the substrate, wherein a sacrificial body, in the liquidupstream of the space, dissolves in the liquid to reduce the rate ofdissolution of a component of (a) the projection system, (b) a substratetable holding the substrate, (c) a liquid supply system providing theliquid, or any combination of (a), (b), and (c).

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a further liquid supply system according to an embodimentof the invention;

FIG. 6 depicts a final element of the projection system with aprotective coating;

FIG. 7 depicts a final element of the projection system and a liquidsupply system for providing a first immersion liquid and a secondimmersion liquid;

FIG. 8 depicts a liquid supply system according to an embodiment of thepresent invention;

FIG. 9 depicts a protective plate applied to the final element of aprojection system according to an embodiment of the invention;

FIG. 10 depicts a protective plate and liquid layer applied to the finalelement of a projection system according to an embodiment of theinvention; and

FIG. 11 depicts a two layer protective coating applied to the finalelement of a projection system according to an embodiment of theinvention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam PB (e.g. UV radiation or DUV radiation).    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PL configured to project a pattern imparted to the radiation        beam PB by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more mask tables). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device (e.g., maskMA), which is held on the support structure (e.g., mask table MT), andis patterned by the patterning device. Having traversed the mask MA, theradiation beam PB passes through the projection system PL, which focusesthe beam onto a target portion C of the substrate W. With the aid of thesecond positioner PW and position sensor IF (e.g. an interferometricdevice, linear encoder or capacitive sensor), the substrate table WT canbe moved accurately, e.g. so as to position different target portions Cin the path of the radiation beam PB. Similarly, the first positioner PMand another position sensor (which is not explicitly depicted in FIG. 1)can be used to accurately position the mask MA with respect to the pathof the radiation beam PB, e.g. after mechanical retrieval from a masklibrary, or during a scan. In general, movement of the mask table MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the mask table MT may be connected to ashort-stroke actuator only, or may be fixed. Mask MA and substrate W maybe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2. Although the substrate alignment marks as illustratedoccupy dedicated target portions, they may be located in spaces betweentarget portions (these are known as scribe-lane alignment marks).Similarly, in situations in which more than one die is provided on themask MA, the mask alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the mask table MT and the substrate table WT are keptessentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the mask table MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the masktable MT may be determined by the (de-)magnification and image reversalcharacteristics of the projection system PL. In scan mode, the maximumsize of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the mask table MT is kept essentially stationaryholding a programmable patterning device, and the substrate table WT ismoved or scanned while a pattern imparted to the radiation beam isprojected onto a target portion C. In this mode, generally a pulsedradiation source is employed and the programmable patterning device isupdated as required after each movement of the substrate table WT or inbetween successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Another solution which has been proposed is to provide the liquid supplysystem with a seal member which extends along at least a part of aboundary of the space between the final element of the projection systemand the substrate table. The seal member is substantially stationaryrelative to the projection system in the XY plane though there may besome relative movement in the Z direction (in the direction of theoptical axis). A seal is formed between the seal member and the surfaceof the substrate. In an embodiment, the seal is a contactless seal suchas a gas seal. Such as system with a gas seal is disclosed in U.S.patent application Ser. No. 10/705,783, hereby incorporated in itsentirety by reference.

FIG. 5 shows a liquid reservoir 10 between the projection system PL anda substrate W which is positioned on the substrate stage WT. The liquidreservoir 10 is filled with a liquid 11 having a relatively highrefractive index, e.g. water, provided via inlet/outlet ducts 13. Theliquid has the effect that the radiation of the projection beam is ashorter wavelength in the liquid than in air or in a vacuum, allowingsmaller features to be resolved. It is well known that the resolutionlimit of a projection system is determined, inter alia, by thewavelength of the projection beam and the numerical aperture of thesystem. The presence of the liquid may also be regarded as increasingthe effective numerical aperture. Furthermore, at fixed numericalaperture, the liquid is effective to increase the depth of field.

The reservoir 10 forms, in an embodiment, a contactless seal to thesubstrate W around the image field of the projection system PL so thatthe liquid is confined to fill the space between the substrate's primarysurface, which faces the projection system PL, and the final element(e.g. an ‘abschlussplatte’ which seals the projection system, or thefinal optical element of the projection system) of the projection systemPL. The reservoir is formed by a seal member 12 positioned below andsurrounding the final element of the projection system PL. Thus, theliquid supply system provides liquid on only a localized area of thesubstrate. The seal member 12 forms part of the liquid supply system forfilling the space between the final element of the projection system andthe substrate W (or, e.g., a sensor) with a liquid. This liquid isbrought into the space below the projection system and within the sealmember 12. The seal member 12 extends a little above the bottom elementof the projection system and the liquid rises above the final element sothat a buffer of liquid is provided. The seal member 12 has an innerperiphery that at the upper end closely conforms to the shape of theprojection system or the final element thereof and may, e.g. be round.At the bottom the inner periphery forms an aperture which closelyconforms to the shape of the image field, e.g. rectangular, though thisis not necessarily so. The projection beam passes through this aperture.

The liquid 11 is confined in the reservoir 10 by a seal device 16. Asillustrated in FIG. 5, the seal device is a contactless seal, i.e. a gasseal. The gas seal is formed by gas, e.g. air or synthetic air, providedunder pressure via inlet 15 to the gap between seal member 12 andsubstrate W and extracted by first outlet 14. The over pressure on thegas inlet 15, vacuum level on the first outlet 14 and the geometry ofthe gap are arranged so that there is a high-velocity gas flow inwardstowards the optical axis of the apparatus that confines the liquid 11.As with any seal, some liquid is likely to escape, for example up thefirst outlet 14.

FIGS. 2 and 3 also depict a liquid reservoir defined by inlet(s) IN,outlet(s) OUT, the substrate W and the final element of projectionsystem PL. Like the liquid supply system of FIG. 5 the liquid supplysystem illustrated in FIGS. 2 and 3, comprising inlet(s) IN andoutlet(s) OUT, supplies liquid to a space between the final element ofthe projection system and a localized area of the primary surface of thesubstrate.

Both of the liquid supply systems of FIGS. 2 & 3 and FIG. 5 as well asother solutions, such as a bath in which the substrate W or wholesubstrate table WT is immersed and the liquid supply system of FIG. 4described hereafter, may be used with the present invention describedbelow.

FIG. 6 illustrates in detail the final element 20 of the projectionsystem PL. In the embodiment illustrated in FIG. 6 the final element isa final optical element 20 which comprises a first component 25 and asecond component 27. The final element 20 of the projection system PLcomprises first and second components 25, 27 so that the element may bemade of a material which exhibits birefringence. An example material forirradiation at 157 nm is CaF₂ which is transmissive but exhibitsbirefringence properties at this wavelength. Quartz is barelytransmissive at 157 nm. CaF₂ is also useful for 193 nm although quartzcan also be used at this wavelength. However, quartz lenses suffer fromcompaction at these wavelengths which can cause radiation to be focusedon to small bits of the lens which discolor (go dark) and absorb moreheat and so a channel can get cut.

By providing the final element 20 as first and second components orparts, the birefringence exhibited by CaF₂ at 157 nm can be compensatedfor by ensuring that the crystal orientations of the first and secondcomponents are aligned such that the intrinsic birefringence exhibitedby the first component 25 is cancelled or reduced by the intrinsicbirefringence exhibited by the second component 27. In this way, theprojection beam PB which passes first through the first component 25 andthen through the second component 27 exits the second component 27substantially free of birefringence phenomena.

The remaining optical elements of the projection system PL may becomprised of materials other than CaF₂. The intensity of the projectionbeam is highest at the last element which is also the smallest so thatit is this element which is most likely to suffer from compaction ifmade of quartz.

As illustrated in FIG. 6, the final element 20 of the projection systemPL is substantially hemispherical in shape. Thus, the second component27 is in the shape of a hemisphere and is positioned in a recess of thefirst component 25 which has an outer surface of the shape of ahemisphere with a recess in its non-curved surface.

CaF₂ may dissolve or react with immersion liquid 11 used in an immersionliquid lithographic projection apparatus. Presently the immersion liquidis envisaged as comprising substantially water for 248 nm and 193 nm.For 157 nm, perfluouro-hydrocarbons are envisaged.

One way of protecting the final element 20 of the projection system fromattack by the immersion liquid 11 is to provide a protective coating 40on a surface of the final element 20 which is in contact with theimmersion liquid. In an embodiment, the material of the protectivecoating 40 is inert in the immersion liquid 11 and does not dissolve. Asis illustrated in FIG. 6, the protective coating 40 is attached to thebottom (as illustrated) surface of the second component 27 of theprojection system PL.

In an embodiment, the protective layer is made as thin as possible whilestill providing protection to the final optical element 20 of theprojection system PL. In an embodiment, the protective coating isbetween 5 and 500 nm thick, or between 10 and 200 nm thick. In anembodiment, the material of the protective coating 40 is a metal, ametal oxide or nitride or SiO2 with a low contact angle with theimmersion liquid to limit bubble inclusion. The layer may be depositedon the element 20 by e.g. evaporation, sputtering, etc.

The use of a protective coating 40 is not limited to the case where thefinal element 20 of the projection system PL is comprised of CaF₂. Forexample, if the final element is comprised of quartz (as typically inthe case of an abschlussplatte being the final element), there may alsobe problems due to the dissolution or reaction of quartz with theimmersion liquid 11. In this case a protective layer 40 may also beused.

The protective coating 40 should be as thin as possible to minimizetransmission losses. The refractive index of the protective coating 40can be partially varied by the deposition process and the depositionparameters. Experience gained in the deposition of EUV coatings might beusefully harnessed to optimize this process.

FIG. 7 illustrates a second embodiment of the present invention which isthe same as the embodiment described above except as described below.

In this embodiment the liquid supply system comprises a mechanism toprovide a first immersion liquid 70 which is in contact with the finalelement 20 of the projection system. A second immersion liquid 75 isalso provided which is in contact with the substrate W.

The first immersion liquid 70 can be chosen such that it only reactswith or dissolves very slowly the material of the final element 20 ordoes not react at all. The second immersion liquid 75 can then be chosenbecause of its good optical properties without any activity limitationsbeing placed on it because of its contact with the final element 20.

There are several ways that the two immersion liquids 70, 75 may beprovided to the correct areas of the space and kept substantially apart.For example, it may be possible to provide two sets of inlets andoutlets to give two flows of liquid, especially if the first and secondimmersion liquids are immiscible or not easily mixed.

In the embodiment illustrated in FIG. 7, a membrane 50 is provided forseparating the first and second 70, 75 immersion liquids. The immersionliquids 70, 75 may then be provided separately on either side of themembrane.

In an embodiment, the membrane is between 0.1 and 5 mm thick to give therequired stiffness without seriously deleteriously affecting the qualityof the projection beam PB. A suitable material for making the membrane50 is SiO2. The membrane 50 may be replaceable.

FIG. 8 illustrates a liquid supply system which may be used with eitherof the above two embodiments. The liquid supply system 100 providesliquid from an inlet 102 to a liquid containment system, for example,for use with or used in the types of liquid supply systems illustratedin FIGS. 2 to 5. In the FIG. 8 embodiment, the immersion liquid isprovided between the abschlussplatte 90 and the substrate W. Immersionliquid exits then via a drain 104.

Components of the liquid supply system, the projection system PL and thesubstrate table WT all come in contact with the immersion liquid. If anyof those components are made of a material which can dissolve inuntreated immersion liquid, and are not protected, this candeleteriously affect the lifetime of the apparatus.

In order to address this problem a sacrificial unit 80 is providedupstream of the liquid containment system (for example, seal member 12)in the liquid supply system 100. In the sacrificial unit 80, at leastone sacrificial body 85 is positioned. The sacrificial body 85 isintended to dissolve in the immersion liquid to reduce the activity ofthe immersion liquid with materials of the components to be protected inthe projection system and/or of the substrate table and/or of the liquidsupply system downstream.

For example, if the final element of the projection system PL, e.g. anabschlussplatte 90 (last lens element), is comprised of quartz and is incontact with the immersion liquid, if at least one of the sacrificialbodies 85 is comprised of quartz, the immersion liquid (which may bewater) can be saturated with quartz as it passes through the sacrificialunit 80 such that the immersion liquid activity with quartz once itreaches the liquid containment system and abschlussplatte 90 is reduced.

The sacrificial unit 80 may contain a plurality of sacrificial bodieswhich are not necessarily all of the same material. It may also be thatthe sacrificial bodies may be made of a different material to thosematerials which they are intended to protect. For example, a sacrificialbody may be designed to reduce the pH of the immersion liquid to such alevel that materials of components to be protected downstream of thesacrificial unit 80 do not dissolve. Alternatively, a buffer could beadded to the liquid.

In an embodiment, the sacrificial bodies 85 have as large as possible asurface area to volume ratio. Example shapes are rods, tubes, etc.However, clearly any shape may be used.

In a further embodiment of the invention, shown in FIG. 9, the finalelement 20 of the projection system is protected by a fused silica plate45. This plate may have a thickness in the range of from 50 μm to 5 mmand may be contact bonded or glue bonded to the final element 20. Incontact bonding, no glue is used—the bonding surfaces are made smoothand clean enough to directly bond together. After bonding to the finalelement, the fused silica plate may be ground and polished to thedesired thickness, avoiding difficulties inherent in handling a verythin plate. A liquid-tight seal 46 may be provided around the perimeterof the joint.

A seal 46 around the joint of the final element and the fused silicaprotective plate may be desirable where the final element and the fusedsilica plate are contact bonded together. Although this form of bondingcan provide an exceptionally strong bond, where dissimilar materials,such as CaF₂ and fused silica, are bonded, temperature changes andthermal gradients may cause the bond to “breathe”—differential thermalexpansion or contraction of the two materials causes them to separateuntil the stress is relieved. Although the bond usually reforms veryquickly in the case of thermal separation, if this occurs when the finalelement is in contact with a liquid, e.g. during polishing or grindingof the protective layer or use of the apparatus, liquid can be drawninto the gap.

One form of seal that may be used is a layer of SiO formed by applying asuitable precursor (such as silicone fluids (i.e. comprising Si—O chainsof various lengths with various hydrocarbon side-chains), tetraethylorthosilicate, decamethyl tetrasiloxane and tetrabutyl orthosilicate)and irradiating it with DUV light to photo-convert the precursor to SiO.This form of seal has the advantage that it has a similar hardness tothe fused silica plate and so polishes at a similar rate.

Another form of seal that is useful is a silicon caulk provided over alayer of titanium oxide. The titanium oxide is applied by painting aprecursor onto the seal and photo-converting it to titanium oxide andacts to protect the silicone caulk from UV light during operation of theapparatus.

A further form of seal is formed by painting tetraethyl orthosilicatearound the joint, which then decomposes at room temperature to form athin layer of fused silica which forms a seal. This seal is howeverrather brittle so that careful handling is required.

In a variant of the FIG. 9 arrangement shown in FIG. 10, a liquid 47,such as oil, is provided between the last lens element 20 and theprotective plate 45. In an embodiment, the liquid 47 has a refractiveindex as close as possible to that of the immersion liquid 11, which maybe water, but is not damaging to the material of the final lens element20, which may be CaF₂. This enables the protective plate to beinterchangeable by substantially reducing the requirements on theaccuracy with which the protective plate 45 must be positioned as thefluids above and below it have similar refractive indices.

A further variant, shown in FIG. 11, uses a two layer protectivecoating, made up of inner layer 48 and outer layer 49. It may be verydifficult to form a layer of protective coating without pinholes. Eventhe smallest pinhole in a protective coating applied to a CaF₂ bodyallows dissolution of the CaF₂ body when immersed in liquid (e.g.,water), causing cavitation which is extremely deleterious to the opticalproperties of the element. By the use of a two layer protective coating,it can be arranged that the pinholes in one layer do not match up withthe pinholes in the other layer so that there is no through path in theprotective layer. It can best be ensured that the pinholes of the twolayers do not match up by applying the two protective layers bydifferent methods.

An embodiment of the invention has a first layer 48 of SiO applied bysputtering and a second layer 49 applied by spin coating a precursor andphoto-converting the precursor to SiO. This method may be more effectivethan sputtering two layers of SiO since the pinholes in the secondsputtered layer have a tendency to line up with those in the firstlayer. Surprisingly, the spin coating and photo-conversion method mayprovide a layer of bulk SiO rather than porous SiO. A layer formed byspin-coating a precursor and then photo-converting it to SiO may also beused on its own as a seal layer.

The precursor used to form protective layer 49 may be any suitable fluidof, or containing, organo-silicon compounds. Suitable examples aresilicone fluids (i.e. comprising Si—O chains of various lengths withvarious hydrocarbon side-chains), tetraethyl orthosilicate, decamethyltetrasiloxane and tetrabutyl orthosilicate. The material may be chosento have a desired viscosity to enable a suitably even layer to beprovided by spin coating. Solvents, such as volatile organic solvents,may be used to adjust the viscosity if necessary.

Photo-conversion of the precursor to SiO can be achieved withirradiation by DUV light of various wavelengths, e.g. 184 nm or 172 nm,at a rate determined to avoid any deleterious effects that might beinduced by thermal gradients in the element.

Each of the two layers of the protective coating may have a thickness inthe range of 50 to 200 nm.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

In European Patent Application No. 03257072.3, the idea of a twin ordual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting the substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus may have only one table movable between exposure andmeasurement positions.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substrateusing a projection system and having a liquid supply system configuredto at least partly fill a space between the projection system and thesubstrate with a liquid, wherein an element of the projection systemthrough which the pattern is projected has, on a surface configured tobe in contact with the liquid, a protective coating which issubstantially insoluble in the liquid.

In an embodiment, the protective coating has a thickness equal to orgreater than 5 nm. In an embodiment, the protective coating has athickness less than or equal to 500 nm. In an embodiment, the protectivecoating is a metal, a metal oxide or nitride, CaF₂, SiO, SiO₂ or anycombination of these materials. In an embodiment, the protective coatingis a fused silica plate. In an embodiment, the fused silica plate has athickness in the range of from 50 μm to 5 mm. In an embodiment, thefused silica plate is attached to the element by contact bonding withoutglue. In an embodiment, the protective coating has two distinct layers.In an embodiment, the two distinct layers are of the same material buthave been formed by different methods. In an embodiment, one of the twodistinct layers is formed by sputtering and the other of the twodistinct layers is formed by spin coating a precursor onto the elementand irradiating the precursor with ultraviolet light. In an embodiment,the protective coating is formed by spin coating a precursor onto theelement and irradiating the precursor with ultraviolet light. In anembodiment, the precursor comprises an organo-silicon compound. In anembodiment, the precursor comprises one or more compounds selected fromthe group comprising silicone fluids, tetraethyl orthosilicate,decamethyl tetrasiloxane and tetrabutyl orthosilicate.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substrateusing a projection system and having a liquid supply system configuredto at least partly fill a space between the projection system and thesubstrate with a liquid, wherein the liquid supply system is configuredto provide a first liquid in the space in contact with an element of theprojection system through which the pattern is projected and to providea second liquid in the space in contact with the substrate.

In an embodiment, the liquid supply system further comprises a membraneconfigured to separate the first and second liquids. In an embodiment,the membrane is quartz. In an embodiment, the membrane has a thicknessin the range of 0.1 to 5 mm. In an embodiment, the element comprisesCaF₂. In an embodiment, elements of the projection system other than theelement are made of a material other than CaF₂. In an embodiment, theelement comprises a first and a second component, both componentscomprising CaF₂, wherein the projected pattern passes through the firstcomponent before passing through the second component. In an embodiment,the first and second components each have crystal axes which are alignedsuch that intrinsic birefringence of the first component is compensatedfor by intrinsic birefringence of the second component. In anembodiment, the first and second components are concentric. In anembodiment, the second component is positioned substantially within arecess in the first component.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substrateusing a projection system and having a liquid supply system configuredto at least partly fill a space between the projection system and thesubstrate with a liquid, wherein an element of the projection systemthrough which the pattern is to be projected and configured to be atleast in part in contact with the liquid, comprises first and secondcomponents of CaF₂, SiO₂ or a combination of both materials, thecomponents being arranged such that the projected pattern passes throughthe first component before passing through the second component.

In an embodiment, the first and second components each have crystal axeswhich are aligned such that intrinsic birefringence of the firstcomponent is compensated for by intrinsic birefringence of the secondcomponent. In an embodiment, the first and second components areconcentric. In an embodiment, the second component is positionedsubstantially within a recess in the first component. In an embodiment,elements of the projection system other than the element are made of amaterial other than CaF₂.

In an embodiment, there is provided a lithographic projection apparatusarranged to project a pattern from a patterning device onto a substrateusing a projection system and having a liquid supply system configuredto at least partly fill a space between the projection system and thesubstrate with a liquid, wherein the liquid supply system comprises asacrificial body, in the liquid upstream of the space, configured todissolve in the liquid to reduce the rate of dissolution of a componentof (a) the projection system, (b) the substrate table, (c) the liquidsupply system, or any combination of (a), (b), and (c).

In an embodiment, the sacrificial body is made of substantially the samematerial as the component. In an embodiment, the sacrificial bodycomprises quartz or CaF₂. In an embodiment, the sacrificial body has ashape with a high surface area to volume ratio.

In an embodiment, there is provided a device manufacturing methodcomprising projecting a patterned beam of radiation onto a substratethrough a liquid provided in a space between an element of a projectionsystem and the substrate, wherein a surface of the element in contactwith the liquid comprises a protective coating which is substantiallyinsoluble in the liquid.

In an embodiment, the protective coating has a thickness in the range offrom 5 nm to 500 nm. In an embodiment, the protective coating is ametal, a metal oxide or nitride, CaF₂, SiO, SiO₂ or any combination ofthese materials. In an embodiment, the protective coating is a fusedsilica plate having a thickness in the range of from 50 μm to 5 mm. Inan embodiment, the fused silica plate is attached to the element bycontact bonding without glue. In an embodiment, the protective coatinghas two distinct layers. In an embodiment, the two distinct layers areof the same material but have been formed by different methods. In anembodiment, one of the two distinct layers is formed by sputtering andthe other of the two distinct layers is formed by spin coating aprecursor onto the element and irradiating the precursor withultraviolet light. In an embodiment, the protective coating is formed byspin coating a precursor onto the element and irradiating the precursorwith ultraviolet light.

In an embodiment, there is provided a device manufacturing methodcomprising projecting a patterned beam of radiation onto a substratethrough a first liquid and a second liquid provided in a space betweenan element of a projection system and the substrate, wherein the firstliquid is in contact with the element and the second liquid is incontact with the substrate.

In an embodiment, a membrane separates the first and second liquids. Inan embodiment, the membrane is quartz. In an embodiment, the membranehas a thickness in the range of 0.1 to 5 mm. In an embodiment, the firstliquid is immiscible in the second liquid.

In an embodiment, there is provided a device manufacturing methodcomprising projecting a patterned beam of radiation onto a substratethrough a liquid provided in a space between an element of a projectionsystem and the substrate, wherein the element is at least in part incontact with the liquid and comprises first and second components ofCaF₂, SiO₂ or a combination of both materials, the components beingarranged such that the patterned beam of radiation passes through thefirst component before passing through the second component.

In an embodiment, elements of the projection system other than theelement are made of a material other than CaF₂. In an embodiment, thefirst and second components each have crystal axes which are alignedsuch that intrinsic birefringence of the first component is compensatedfor by intrinsic birefringence of the second component. In anembodiment, the first and second components are concentric. In anembodiment, the second component is positioned substantially within arecess in the first component.

In an embodiment, there is provided a device manufacturing methodcomprising projecting a patterned beam of radiation onto a substratethrough a liquid provided in a space between an element of a projectionsystem and the substrate, wherein a sacrificial body, in the liquidupstream of the space, dissolves in the liquid to reduce the rate ofdissolution of a component of (a) the projection system, (b) a substratetable holding the substrate, (c) a liquid supply system providing theliquid, or any combination of (a), (b), and (c).

In an embodiment, the sacrificial body is made of substantially the samematerial as the component. In an embodiment, the sacrificial bodycomprises quartz or CaF₂. In an embodiment, the sacrificial body has ashape with a high surface area to volume ratio.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

The present invention can be applied to any immersion lithographyapparatus, in particular, but not exclusively, to those types mentionedabove.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

The invention claimed is:
 1. An exposure apparatus, comprising: a liquidsupply system configured to at least partly fill a space, adjacent asubstrate table to hold a substrate, with a liquid; and a projectionsystem to project a patterned radiation beam onto the substrate, theprojection system having an optical element, the optical element havinga bottom surface through which the pattern is projected and a sidesurface extending away from the bottom surface, wherein the bottomsurface and the side surface are in contact with the liquid at leastduring exposure and wherein at least a part of the side surface has aprotective layer, wherein the liquid supply system comprises a liquidconfinement member having a surface extending above the bottom surfaceof the optical element and between which surface extending above thebottom surface of the optical element and the side surface of theoptical element liquid enters at least during exposure and the liquidconfinement member having a bottom surface above the substrate table, atleast part of the liquid confinement member extending below the bottomsurface of the optical element and above the substrate table to definean aperture through which the patterned beam and liquid passes at leastduring exposure and the liquid confinement member comprising an outlet,in the bottom surface of the liquid confinement member, to removeliquid.
 2. The apparatus of claim 1, wherein the protective layerextends upward and outward relative to the bottom surface.
 3. Theapparatus of claim 2, wherein the side surface extends upward anddiverges angularly outward from the bottom surface.
 4. The apparatus ofclaim 1, wherein the liquid supply system comprises an inlet to supplythe liquid, the inlet located above the aperture.
 5. The apparatus ofclaim 4, wherein the inlet is located below the bottom surface of theoptical element.
 6. The apparatus of claim 1, wherein the protectivelayer comprises a coating on the optical element.
 7. The apparatus ofclaim 1, wherein the protective layer has a thickness in the range of 5to 500 nm.
 8. The apparatus of claim 1, wherein the optical element isof SiO₂.
 9. An exposure apparatus comprising: a projection system toproject a patterned beam of radiation onto an object, the projectionsystem comprising a final optical element through which the patternpasses from one side of the final optical element to the object disposedon another side of the final optical element; and a liquid supply systemto at least partly fill a space between the final optical element andthe object with a liquid such that the liquid contacts the object andthe final optical element, wherein at least a surface of the finaloptical element through which the pattern does not pass has a protectivecoating to separate the portion of the final optical element covered bythe coating from the liquid, wherein the liquid supply system comprisesa liquid confinement member having a surface extending above a bottomsurface of the final optical element and between which surface extendingabove the bottom surface of the final optical element and the surface ofthe final optical element liquid enters at least during exposure and theliquid confinement member having a bottom surface above the object, atleast part of the liquid confinement member extending below the bottomsurface of the final optical element and above the object to define anaperture through which the patterned beam and liquid passes at leastduring exposure and the liquid confinement member comprising an outlet,in the bottom surface of the liquid confinement member, to removeliquid.
 10. The apparatus of claim 9, wherein the protective coatingextends outward relative to a surface of the final optical elementthrough which the pattern passes.
 11. The apparatus of claim 10, whereinthe surface of the final optical element extends upward and divergesangularly outward from the surface of the final optical element throughwhich the pattern passes.
 12. The apparatus of claim 9, wherein theliquid supply system comprises an inlet to supply the liquid, the inletlocated above the aperture.
 13. The apparatus of claim 12, wherein theinlet is located below the bottom surface of the optical element. 14.The apparatus of claim 9, wherein the protective coating extends on asurface of the optical element nearest the object and wherein thesurface of the protective coating, on the surface of the optical elementnearest the object, that contacts the liquid is continuous anduninterrupted.
 15. The apparatus of claim 9, wherein the protectivecoating has a thickness in the range of 5 to 500 nm.
 16. A devicemanufacturing method, comprising: at least partly filling a spacebetween an optical element of a projection system and a substrate with aliquid; and projecting a pattern from a patterning device, through theliquid, onto a substrate using the projection system, wherein theoptical element has a bottom surface through which the pattern isprojected and a side surface extending away from the bottom surface,wherein the bottom surface and the side surface are in contact with theliquid and wherein at least a part of the side surface has a protectivelayer; and at least partly confining the liquid using a liquidconfinement member having a bottom surface above the substrate andhaving a surface extending above the bottom surface of the opticalelement between which surface extending above the bottom surface of theoptical element and the side surface of the optical element there isliquid, wherein at least part of the liquid confinement member extendsbelow the bottom surface of the optical element and above the substrateto define an aperture through which the patterned beam and liquidpasses; and removing liquid using an outlet in the bottom surface of theliquid confinement member.
 17. The method of claim 16, wherein theprotective layer extends upward and outward relative to the bottomsurface.
 18. The method of claim 17, wherein the side surface extendsupward and diverges angularly outward from the bottom surface.
 19. Themethod of claim 16, wherein the protective layer comprises a coating onthe optical element.
 20. The method of claim 16, further comprisingsupplying the liquid using an inlet located above the aperture.